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Classifying Stars


Classifying Stars The Hertzsprung-Russell Diagram (H-R Diagram) Graph plotting the surface temperatures of stars against their luminosity (total energy given off each ... – PowerPoint PPT presentation

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Title: Classifying Stars

Classifying Stars
  • The Hertzsprung-Russell Diagram (H-R Diagram)
  • Graph plotting the surface temperatures of stars
    against their luminosity (total energy given off
    each second)
  • Diagonal band that goes from upper left to lower
    right is the MAIN-SEQUENCE STARS
  • The Sun is a main sequence star

Classifying Stars continued
  • Supergiants very luminous, large stars red
    supergiants are the largest stars
  • Giants highly luminous, large stars
  • Dwarfs small, dim stars
  • White dwarfs very faint, very dense, very small

Classifying Stars continued
  • Variable stars vary in brightness over regular
  • Pulsating stars change in brightness as they
    expand (cool, dim) and contract (hot, bright)
  • Cepheid variables the longer their cycle is the
    larger their absolute magnitude is
  • Eclipsing binary 2 stars of unequal brightness
    that revolve around each other and appear to
    change brightness
  • Pulsars emits bursts of radio waves and light
  • They are neutron stars formed in supernovas
  • They produce radio pulses because they rotate
    very rapidly

LT 9 I can describe how a protostar becomes a
Birthplace of Stars
  • Begins as a nebula (a cloud of dust and gas)
  • Diffuse nebula lit up by bright light from
    nearby star (ex Great Nebula in Orion)
  • Dark nebula show up as dark patch (ex Horsehead
    Nebula in Orion

Making a Star
  • Cloud starts compressing and particles are pulled
    closer to each other by gravity and temperature
  • Hot areas start to glow (protostars) and continue
  • Eventually they contract enough to trigger fusion
    and hydrogen into helium which gives off huge
    amounts of energy (star)
  • When the energy released counterbalances gravity,
    the star stops contracting (main-sequence star)

LT 10 I can explain how a main-sequence star
generates energy.
Stable State
  • Nuclear fusion is what fuels a stars energy
  • Hydrogen fuses to Hydrogen to form Helium
  • When Hydrogen in core is used up, gravity causes
    the core to collapse
  • Temperature rises making the outer shell of the
    star super expand
  • The surface temperature drops and it is now a
    huge, bright, red aging star

LT 11 I can describe the evolution of a star
after is main-sequence stage.
Red Giant (Red Supergiant)
  • When all the fuel for fusion is used up the giant
    star collapses into a small, dense, dying star of
    low luminosity and high temperature
  • Red Supergiants have a mass 7 times the Suns
  • When a red supergiant starts to collapse, there
    is a huge explosion (supernova) everything
    except the stars core is blown out into space
  • What is left of the core becomes a very dense,
    invisible pulsar
  • This pulsar eventually stops and becomes a
    neutron star

Red Supergiants
Supernova Explosion
White Dwarf
  • Cools, turns dull red and shines its leftover
    heat energy into space
  • May be hit by another star causing it to flare up
    temporarily (Nova)

White Dwarf
? Nova Image
Black Dwarf
  • Final Stage in a stars life
  • Neutrons collapse into a very small volume with
    huge gravitational forces
  • Cold, dark dead star
  • Nothing can escape
  • Ex Cygnus X-1

Black Dwarf
The Sun
  • An average medium-sized star
  • Stable main-sequence star for approximately 5
    billion years
  • Should continue to shine steadily for another 5
    billion years before its hydrogen supply is used